A hybrid electrical vehicle (HEV) refers to a vehicle equipped with two types of power sources, i.e., a thermal power source (generating power by a conventional gasoline engine or diesel engine) and an electric power source (generating power by a battery and an electric motor). With disposing the electric motor in the hybrid electrical vehicle, the power system can be adjusted flexibly according to the practical working conditions of the hybrid electrical vehicle and the engine can keep working in regions with the optimum comprehensive properties, thus reducing the oil wear and the emission.
Some of the existing hybrid electrical vehicles adopt a series-parallel hybrid power system, which is characterized by disposing one mechanical gear shifting mechanism in the internal combustion engine system and the electric motor drive system respectively. The two mechanical gear shifting mechanisms are connected via a planetary wheel structure, such that the rotating speed relationship between the internal combustion engine system and the electric motor drive system can be adjusted synthetically.
However, the driving mode of the conventional hybrid electrical vehicle is simplex and the driver cannot select the driving mode according to individual driving habits, the long term and constant driving condition. For example, considering that Asians often live in concentrated districts and have a relatively constant driving path to and from work which is mostly less than 50 km, it is very appropriate to drive in a pure electric mode. However, the conventional hybrid electrical vehicle reduces the oil wear by adjusting the engine via the electric motor instead of eliminating the oil wear totally. Therefore, the conventional hybrid electrical vehicle generally does not have the manual electrical vehicle (EV) mode switching function. Even if the conventional electrical vehicle has the manual EV mode switching function, the pure electric driving mileage of the vehicle is short due to the limitation of the electric quantity of the battery.
Moreover, since the purpose of the conventional hybrid electrical vehicle is to reduce the oil wear, the electric motor and engine with a high power and a high torque will not be selected, and thus the power performance of the hybrid electrical vehicle is low and the driving fun is greatly reduced. For example, some hybrid electrical vehicles take more than 10 s to accelerate from 0 to 100 km/h and provide a poor high speed performance.
Furthermore, some conventional hybrid electrical vehicles adopt the series-parallel structure and the method for controlling the series-parallel structure, and the strategy in which the engine drives the vehicle solely does not exist. In other words, even if in the relatively economical working regions, the engine still charges the battery via a first electric motor MG1 and adjusts the rotating speed thereof via the first electric motor MG1 to implement the gear shift; moreover, in the heavy load acceleration condition, due to the limitation of the battery capacity, only if a part of the power of the engine is used to drive the first electric motor MG1 to generate power, can the engine provide the electric energy to the second electric motor MG2 together with the battery. The above facts reduce the driving efficiency of the engine. In addition, in the engine stop-start strategy, the predetermined demanded power and speed threshold are relatively low, and the speed switching condition is set as a point instead of an internal, thus resulting in a premature and frequent start of the engine.
In addition, some conventional hybrid electrical vehicles do not adopt the plug-in structure due to the small capacity of the battery, and the electric quantity of the battery is converted from the gasoline totally, thus increasing the cost. Moreover, the series-parallel structure is complex and it is difficult to match with the Electronic Continuously Variable Transmission (ECVT), and the cost is high.